After having sex on the 2nd day i started feeling...

Dear Customer
Welcome, and thank you for trusting us
Regarding your question
There are many causes of lower abdominal pain which its
First: surgical causes like:
1.   Appendicitis
2.    Intestinal obstruction (mechanical obstruction of small bowel )
3.    Hernia (buldge of the abdominal content )
Second: medical causes like:
1.    Acute gastroenteritis
2.    Cohn's disease
3.    Irritable bowel syndrome (IBS )
Third: urological causes like
1.    Kidney stones
2.    Acute urinary tract infection
3.    Glomerulonephritis (inflammation of the kidney )
4.    Pyelonephritis
Gynecological cause:
1.    Ovarian cyst
2.    Pelvic inflammatory disease
3.    Ovarian torsion
You should go to the doctor to take a full medical history from you , them doing   full examination to your abdomen them doing specific laboratory test like :
Cbc
Urine analysis
Stool analysis
pregnancy test
If this abdominal pain associated with :
1.repeated vomiting
2. fever above 38.5
3. severe abdominal pain not relieved
4. vomiting of blood
5. black stools
6. abdominal distention  
You should go to the hospital to evaluate you
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